1 files changed, 158 insertions, 0 deletions
diff --git a/extensions/recv-hole b/extensions/recv-hole
new file mode 100755
index 00000000..fe69f304
--- /dev/null
+++ b/extensions/recv-hole
@@ -0,0 +1,158 @@
+#!/bin/sh
+#
+# Copyright (C) 2014-2015  Codethink Limited
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# =*= License: GPL-2 =*=
+
+
+# Receive a data stream describing a sparse file, and reproduce it,
+# either to a named file or stdout.
+#
+# The data stream is simple: it's a sequence of DATA or HOLE records:
+#
+#    DATA
+#    123
+#    <123 bytes of binary data, NOT including newline at the end>
+#
+#    HOLE
+#    123
+#
+# This shell script can be executed over ssh (given to ssh as an arguemnt,
+# with suitable escaping) on a different computer. This allows a large
+# sparse file (e.g., disk image) be transferred quickly.
+#
+# This script should be called in one of the following ways:
+#
+#    recv-hole file FILENAME
+#    recv-hole vbox FILENAME DISKSIZE
+#
+# In both cases, FILENAME is the pathname of the disk image on the
+# receiving end. DISKSIZE is the size of the disk image in bytes. The
+# first form is used when transferring a disk image to become an
+# identical file on the receiving end.
+#
+# The second form is used when the disk image should be converted for
+# use by VirtualBox. In this case, we want to avoid writing a
+# temporary file on disk, and then calling the VirtualBox VBoxManage
+# tool to do the conversion, since that would involve large amounts of
+# unnecessary I/O and disk usage. Instead we pipe the file directly to
+# VBoxManage, avoiding those issues. The piping is done here in this
+# script, instead of in the caller, to make it easier to run things
+# over ssh.
+#
+# However, since it's not possible seek in a Unix pipe, we have to
+# explicitly write the zeroes into the pipe. This is not
+# super-efficient, but the way to avoid that would be to avoid sending
+# a sparse file, and do the conversion to a VDI on the sending end.
+# That is out of scope for xfer-hole and recv-hole.
+
+
+set -eu
+
+
+die()
+{
+    echo "$@" 1>&2
+    exit 1
+}
+
+
+recv_hole_to_file()
+{
+    local n
+
+    read n
+    truncate --size "+$n" "$1"
+}
+
+
+recv_data_to_file()
+{
+    local n
+    read n
+
+    local blocksize=1048576
+    local blocks=$(($n / $blocksize))
+    local extra=$(($n % $blocksize))
+
+    xfer_data_to_stdout "$blocksize" "$blocks" >> "$1"
+    xfer_data_to_stdout 1 "$extra" >> "$1"
+}
+
+
+recv_hole_to_stdout()
+{
+    local n
+    read n
+    (echo "$n"; cat /dev/zero) | recv_data_to_stdout
+}
+
+
+recv_data_to_stdout()
+{
+    local n
+    read n
+
+    local blocksize=1048576
+    local blocks=$(($n / $blocksize))
+    local extra=$(($n % $blocksize))
+
+    xfer_data_to_stdout "$blocksize" "$blocks"
+    xfer_data_to_stdout 1 "$extra"
+}
+
+
+xfer_data_to_stdout()
+{
+    local log="$(mktemp)"
+    if ! dd "bs=$1" count="$2" iflag=fullblock status=noxfer 2> "$log"
+    then
+        cat "$log" 1>&2
+        rm -f "$log"
+        exit 1
+    else
+        rm -f "$log"
+    fi
+}
+
+
+type="$1"
+case "$type" in
+    file)
+        output="$2"
+        truncate --size=0 "$output"
+        while read what
+        do
+            case "$what" in
+                DATA) recv_data_to_file "$output" ;;
+                HOLE) recv_hole_to_file "$output" ;;
+                *) die "Unknown instruction: $what" ;;
+            esac
+        done
+        ;;
+    vbox)
+        output="$2"
+        disk_size="$3"
+        while read what
+        do
+            case "$what" in
+                DATA) recv_data_to_stdout ;;
+                HOLE) recv_hole_to_stdout ;;
+                *) die "Unknown instruction: $what" ;;
+            esac
+        done |
+        VBoxManage convertfromraw stdin "$output" "$disk_size"
+        ;;
+esac